Generally, fine pattern formation is carried out by photolithography in the manufacture of a semiconductor device. A number of substrates called transfer masks are normally used for such fine pattern formation. The transfer mask comprises generally a transparent glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the transfer mask.
In the manufacture of a transfer mask by photolithography, use is made of a mask blank having a thin film (e.g. a thin film made of a material containing a transition metal) for forming a transfer pattern (mask pattern) on a transparent substrate such as a glass substrate. The manufacture of the transfer mask using the mask blank comprises an exposure process of writing a required pattern on a resist film formed on the mask blank, a developing process of developing the resist film to form a resist pattern in accordance with the written pattern, an etching process of etching the thin film along the resist pattern, and a process of stripping and removing the remaining resist pattern. In the developing process, a developer is supplied after writing the required pattern on the resist film formed on the mask blank to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. In the etching process, using the resist pattern as a mask, an exposed portion of the thin film, where the resist pattern is not formed, is dissolved by dry etching or wet etching, thereby forming a required mask pattern on the transparent substrate. In this manner, the transfer mask is produced.
For miniaturization of a pattern of a semiconductor device, it is necessary to shorten the wavelength of exposure light for use in photolithography in addition to miniaturization of the mask pattern of the transfer mask. In recent years, the wavelength of exposure light for use in the manufacture of a semiconductor device has been shortened from KrF excimer laser light (wavelength: 248 nm) to ArF excimer laser light (wavelength: 193 nm).
As a type of transfer mask, a halftone phase shift mask is known apart from a conventional binary mask having a light-shielding film pattern made of a chromium-based material on a transparent substrate. This halftone phase shift mask is configured to have a phase shift film in the form of a light-semitransmissive film on a transparent substrate. This phase shift film in the form of the light-semitransmissive film is adapted to transmit light having an intensity that does not substantially contribute to exposure (e.g. 1% to 20% at an exposure wavelength) and to provide a predetermined phase difference. The halftone phase shift mask has phase shift portions formed by patterning the phase shift film and light-transmissive portions formed with no phase shift film and adapted to transmit light having an intensity that substantially contributes to exposure. The phase shift film is formed so that the phase of the light transmitted through the phase shift portions is substantially inverted with respect to that of the light transmitted through the light-transmissive portions. As a consequence, the lights having passed near the boundaries between the phase shift portions and the light-transmissive portions and bent into the others' regions due to diffraction cancel each other out. This makes the light intensity at the boundaries approximately zero to thereby improve the contrast, i.e. the resolution, at the boundaries. As a material of the phase shift film, a molybdenum silicide compound, which is a material containing molybdenum and silicon, is widely used.
Further, there is a special type of light-semitransmissive film which is mainly used as a thin film for forming a pattern of an enhancer mask. Light-semitransmissive portions formed by this light-semitransmissive film transmit exposure light at a predetermined transmittance, but different from the halftone phase shift film, the phase of the exposure light transmitted through the light-semitransmissive portions becomes approximately the same as the phase of the exposure light transmitted through light-transmissive portions. Also as a material of this light-semitransmissive film, a molybdenum silicide compound, which is a material containing molybdenum and silicon, is widely used.
Further, in recent years, there has also appeared a binary mask using, as a light-shielding film, a molybdenum silicide compound which is a material containing molybdenum and silicon.